The present invention relates to a method of calibrating a sensor, in particular a yaw rate sensor, in which sensor values and associated temperature values (T) are stored in the shape of reference points in a non-volatile memory of the sensor, in which case the values are determined during a calibration mode in which the sensor is exposed to a predefined temperature profile, and relates to a sensor.
So-called sensor clusters are employed in many cases in motor vehicles with ESP functionality, which contain yaw rate sensors being connected to a separate electronic brake control unit (EBS) via a data bus. A sensor cluster consists of screened housing, yaw rate sensor elements, an electronic processing unit (e.g. microcontroller) and a data bus such as a CAN bus (WO 00/32022).
The sensor cluster makes use of at least one yaw rate sensor, the zero offset error thereof depending on manufacturing tolerance, temperature and ageing. During operation of the sensor, this zero point is responsible for possible inaccuracies of the yaw rate sensor in dependence on temperature.
The yaw rate sensor is calibrated within limits during its manufacture and during its operation with respect to its zero offset error.
FIG. 1 shows the signal processing within the sensor cluster, which is described in WO 01/50090 A1.
During manufacture the sensor cluster is switched into a special calibration mode. Subsequently, the sensor cluster runs through a fixed temperature range in a furnace. As this occurs, the software in the sensor cluster senses the temperature and the zero point of the yaw rate sensor.
The reference points [T, YOffset] are determined from the read-in data and are saved in the non-volatile memory. The calibration mode is left thereafter.
Thus, n-correction positions [Tn, YOffset(n)] are available for the zero point correction of the yaw rate sensor.
During operation of the vehicle, the temperature of the sensor module is constantly measured, and based on this value the zero offset error of the yaw rate sensor is calculated using the stored reference points by way of linear interpolation.
The yaw rate signal sent by way of the CAN bus is calculated from the measured sensor signal and the calculated zero point of the yaw rate sensor according to the following relation:
      Y    cluster    =            Y      Sensor        -          Y      Offset      
When vehicle standstill is detected, the temperature of the sensor module and the yaw rate are measured. These values are allocated to one of the temperature classes stored in a non-volatile memory. A suitable method is used to determine the average value of the already saved zero point of the yaw rate sensor and the newly measured value. The result is stored in the non-volatile memory instead of the old value.
This calibration still does not provide a sufficient rate of accuracy for some special service requirements; hence, there is the demand of further improving the zero offset error.
In view of the above, an object of the invention is to still further improve the accuracy of the calibration of the sensor error.